Shane Ross writes well, so the book is a fairly smooth and engaging read. The problem is content and orientation. As a disclaimer to go with my less than positive review of the book, I can say that I wouldn't ever vote Sinn Fein so I am certainly not an apologist for them.
Throughout the book, any actions by Sinn Fein are presented conspiratorially, even where such behaviour is completely normal for a political party. For example the author repeatedly implies that selecting a middle class Dublin woman as leader is a manipulation, whereas any political party in the same situation would likely do the same, and it is after all the goal of parties to try to win elections so they typically choose someone likely to appeal to electors!
Ross' anxiety to nail SF also causes him to exaggerate. The McDonald family home of 254 square metres hardly qualifies as a mansion, for example. This detracts from the more relevant point that it is not really clear where the Lanigan Mcdonald family would have found enough money to pay for the house, though again the amounts are hardly enormous and there are plenty of examples of far more blatant (and corrupt) financial overreach by some others of our former leaders.
Overall the main relevant question is whether SF is a truly democratic party and thus if its ascent to power could undermine democratic and transparent governance. Here Ross raises many legitimate questions particularly regarding influence of former armed fighters. However his stance is so anti SF and often petty, that these big questions are lost in the diatribe.